Salting out a dialkyl ether of diethylene glycol from an aqueous solution



Dec. 29, 1959 w ssE 2,91

SALTING OUT A DIALKYL ETHER OF DIE LENE GLYCOL FROM AN AQUEOUS SOLUTIFiled 958 July 23, 1

No. 0H

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TWO LIQUID Guenter K. Wei

INVEN ATTORNEYS A tillation.

SALTING OUT A *DIAL KYL 'ETI -IERXOF' DIETH- YLElSIE GLYCOL FRQM AN-AQUEOUS SOLU- TIO I :Gnenter K. Weisse, Niagara Falls, N..,.assignor toOlin Mathieson Chemical Corporation, .a. corporation of VirginiaApplication Julyl}, 19 8 ,.S erial No. 753,390

2 Claims. (Cl. 260-615) This invention relates to the,,e fiicient;separation of certain ethers from aqueous solutions thereof. Moreparticularly it relates to the separation of'diethylene {glycol dialkylethers which have the generic formula .ROCH CH OCH CH OR' wherein R andR are alkyl radicals containing one to 'three carbon atoms each, whichethers are either completely or highly soluble inwater. This applicationis a continuation-in -part of .my copending application Serial No.58l,l88'filed"April 27, 1956 and now abandoned.

These diglycol ethers are generally obtained in aqueous solution byreacting .a saturated aliphatic monohydric alcohol containing one tothree carbon atoms, .such as methanol, ethanol, n-propanol or.isopropanol, and the appropriate dichloro etherin the presence ofanalkali metal hydroxide such as sodium'hydroxide orpotassium hydroxide.For example, bis-(2-methoxyethyl) ether can be made frombis-(Z-chloroethyl) ether. by treating it with methanol and alkali. Ifthe reaction is performed with sodium hydroxide, two molesof sodiumchloride and two moles of water will forrnfor every mole of etherproduced. The salt may be separated from the reaction mixture bycentrifugation or :filtration before the reaction mixture'is distilled.It is not.,economical to decant the supernatant solution from thesaltlayenas the latter is permeated throughout with the solution of theproduct.

The above-mentioned ethersform azeotropes with water and thereforecannot be isolatedv by simple fractional dis- If fractionation is,applied to remove 'the azeotrope'from the reaction mixture, it must bea vacuum fractionation as the atmospheric boiling points of these ethersare high enough to cause side reactions between residual alkali andintermediate monochloroethers which are in solution in the reactionmixture. Under these conditions, low-boiling unsaturated ethers, such asmethoxyethyl vinyl ether, are formed during the'fractionation anddistill with the product. To recover a. pure product, a secondfractionation must'be made using an auxiliary component which forms anazeotrope with water at a relatively low temperature. I 'Even' withvarious cornbinations of such operations, the separation of the aboveethers from water solution has heretofore been a com plex and expensiveprocedure.

The main object of this invention is to provide an improved process forrecovering the aforementioneddiethers from water solution, which etherscan contain as little as one weight percent water or less.

A further object is to provide a step whereby an ether of theabove-defined structure may be separated from aqueous solution as valiquid phase containing a low water content, preferably less than 10 toby weight. Another object is to provide a separation process of improvedefiiciency for the recovery of anether as above-described from anaqueous solution-thereof. Other objects will be apparent from thefollowing description.

The foregoing objects have been accomplished-in accordance with-thisinvention by causing-the separationof ted States Patent? the desiredether as a liquid layer of low water content, which layer readily yieldsthe pure ether when subjected to fractional distillation. Such liquidphase separation has been found to be effected by substantiallysaturating the aqueous solution of the-ether with sodium chloride,potassium chloride ;or other alkali metal chloride and adding an amountof an alkali metal hydroxide or alkali metal carbonate or mixturethereof,rfor example sodium hydroxide, potassium hydroxide, sodiumcarbonate and potassium carbonate, corresponding to about 5% to 35% byweight of the finalmixture, at a temperature between about 0 and, 0,preferably at about 25 Cf'to 60? C. This results in the formation of twoliquid. phases, the lighter or upper phase containing substantiallyall-the ether with only small amounts of water. The water content of theether layer is about 10% to 15% by weight or less, being lower as theamount of alkali metal hydroxide or carbonate is increased.Substantially pure ether is then readily recovered by fractionaldistillation of the separated ether layer, the small content of waterbeing removed in the more volatile fractions Without the loss ofanysubstantial amount of the ether. In contrast, the fractionaldistillation of ether containing substantial amounts 'of Water resultsin the initial removal of water as the waterether azeotrope and thusinvolves the loss of one part by weight of'ether for about each fourparts of water, unless further recovery treatment is applied.

The unpredictable nature of the solubility relationships which-makepossible the efficient process of this invention is verifiedbypublications such as that of Kobe et al., Journal of Physical Chemistry,vol. 44, 629-633 (1940). While the cyclic di-ether, dioxane, was foundto be salted out by sodium chloride and other metal chlorides andelectrolytes, it'was not salted out by fifteen'of thirty-oneelectrolytes which were tested. Thusjthe article-states on page 632 Thetheory of salting out is not well understood, .and no theory has beenadvanced which "will account for all the phenomena involved. I

The above conclusion is supported by experimental observations inconnection with the present invention.

The above-defined ethers do not form a separate liquid phase when sodiumor'potassium chloride is added to aqueous solutions thereof. If an ethersuchhsbis-(ZZ- methoxyethyl) ether is added to concentrated brine,substantially all of the ether goes into solution and salt precipitates.

However, the combined use of an alkali metal chloride substantiallysaturatingthe aqueous ether solution and of an alkali metal hydroxide orcarbonate or'mixture thereof, in an amount of about 5 to 35% by weightof the final mixture, effects the separation of an'insoluble etherliquid phase containing substantially less than 10% to 15% by Weight ofWater. The obtainment of such insoluble other layer was unpredictable asthe combined use with saturated brine of about 8% by Weight of otherelectrolytes including sodium formate, sodium acetate, ammoniumchloride, ammonium sulfate, ammonium hydroxide, borax (Na B O -10H O),and calcium chloride did not result in the separation'of a second liquidlayer. Furthermore, the obtainment of a liquid ether phase by thecombined use of an alkali metal chloride and an alkali metal hydroxideand/or carbonate, which liquid has a water content of substantially lessthan 10% to 15% by weight is a surprising as well as advantageousphenomenon.

In a preferred embodiment of this invention, aqueous or solid alkalimetal hydroxide is added to an aqueous solution of the ether,substantially saturated With an alkali metal chloride, until the finalmixture contains 5 35 percent by Weight of the alkali to effect theseparation of a second liquid phase. Over a 96 percent by Weight ethersolution can be separated from the caustic solution as by siphoning ordecantation after the treatment, if the upper part of this range isemployed. In general, the solubility of the ether in the aqueous phasedecreases as the temperature is increased. However, the separation ispreferably carried out at about 25 to 60 C.

The following examples further illustrate this invention, as does theattached phase diagram in Fig. 1.

Example I A solution of 53 grams of pelletized NaOH and 307 grams of CHOH was added to 429 grams of bis-(2-chlomethyl) ether in a 2-liter,S-necked flask, equipped with an overhead condenser. Heat was applied bymeans of a mantle, the temperature being raised to 73 C. in 2 hours.Beginning at the end of the first 2 hour period, 211 grams of pelletizedNaOH were added to the reaction vessel in increments of 53 grams every 2hours, except for the final increment which was 52 grams. Heating wascontinued for 4 hours following the addition of the last portion ofNaOH. The temperature was maintained between 71 C. and 83 C. throughoutthe reaction time (except for the initial warm-up period of about 35minutes) which totalled about 12 hours and 15 minutes.

Most of the excess methanol was distilled from the reaction mixture anda 300 gram portion of a percent aqueous NaOH solution was added to theremaining reaction mixture with stirring to provide a mixture containingabout 6.8 weight percent of sodium hydroxide. The organic phaseseparated as the uppermost phase and was siphoned off at a temperatureof about 40 C.

The organic layer which was siphoned from the reaction mixture wascompletely separated from a small amount of aqueous phase in aseparatory funnel to give about 380 grams of his (Z-methoxyethyl) etherproduct phase.

This was purified by fractionation at atmospheric pressure after theaddition of 100 grams of tetraline. Several fractions were recoveredoverhead which were:

Gut Grams B.P., 0. Substance 17 65 CH OH. 57 82 85.5 Unidentified. 25 9699 Do. 20 158 462.8 bis-(2-n1ethoxyethyDether. 182 163. 5-164. 5 Do. 55164. 8-165. 5 D0. 28 166 -167. 3 Unidentified.

Example II A mixture of: Grams Beta,beta'-dichlorodiethyl ether 429Methanol 307 Water 36 NaOH (solid) 53 was placed in a kettle fitted witha stirrer and reflux condenser. The mixture was heated to 71 C. andsodium hydroxide pellets were added every half hour. The first threeadditions were of 53 grams each and the final fourth addition 52 Igrams. After 2 hours the pot temperature had risen to about 80 C. Thereaction mixture was then cooled to 50 C. and was placed in a stainlesssteel autoclave equipped with a stirrer. It was held there for 2 hoursat 120 C., About 150 grams of methanol sodium chloride, includedapproximately 269 grams of water and 149 grams of NaOH.

The upper organic phase of 316 grams, containing substantially all ofthe ether product, was siphoned oif. It was fractionally distilled andpure diethylene glycol dimethyl ether was obtained at 56% of thetheoretical yield based on the dichlorodiethyl ether used.

Example 111 A mixture of: Grams Ethyl alcohol 1380Beta,beta-dichlorodiethyl ether 429 NaOH (50% aqueous) 528 was placed inan autoclave and the temperature was maintained at about C. for about llhours and then at about 120 C. for 3 hours. The charge was cooled andtransferred to a vessel together with 395 grams of ethanol which wasused to rinse the bomb. The solid sodium chloride was removed bycentrifugation and was washed with 200 grams of ethanol which were addedto the centrifugate product solution. The latter was then heated and1685 grams of ethanol were removed by distillation. 'The residue wastreated with grams of flake sodium hydroxide after which the upperorganic layer of 273 grams, containing substantially all the etherproduct, was removed. The two-phase mixture, saturated with sodiumchloride, obtained after the addition of the sodium hydroxide contained372 grams of water and 114 grams of NaOH. Fractional distillation of theorganic layer yielded 266 grams of substantially pure diethylene glycoldiethyl ether.

The phase diagram in Figure 1 represents the bis-(Z-methoxyethyl)ether-water-NaOH system and is typical of the systemsformed by an ether as defined above, an alkali metal hydroxide orcarbonate and water. Although the determinations were carried out withmixtures saturated with sodium chloride to simulate actual processconditions, the compositions are represented on a saltfree basis tosimplify the diagram.

The phase diagram indicates, at point Z, that less than 1 percent NaOHis required to separate 2 liquid phases from a mixture which contains 50percent or more ether. As this binodal curve is followed to the left,the water layer loses ether to the ether layer until at point Y theaqueous layer contains less than 1 percent ether. The conjugate phase,obtainedby following the tie-line from point Y, comprises over 97percent ether and less than 3 percent water.

Under reaction conditions which are variations of the proceduredescribed in Example I, the reaction mixture at the time when the phasesare separated from each other can contain from approximately 25 to 70percent by weight of water, based upon the weight of the water andether, for example, a composition close to the point Z. At equilibrium,in the presence of over 5% by weight of caustic soda in the mixture, theaqueous layer contains a small amount of the ether and the ether layercontains 10% to 15% water or less, such contents being decreased as thepercentage of caustic soda in the mixture is increased. It is apparentthat separation of the other is much more simple and less costly by theprocedure of this invention than would be the distillation of the 20percent ether azeotrope, followed by isolation of the ether from theazeotrope.

I claim:

1 In the separation of a dialkyl ether of diethylene glycol, wherein thealkyl groups contain one to three carbonatoms each, from an aqueoussolution thereof, the process comprising substantially saturating saidsolution with an alkali metal chloride, admixing a material chosen fromthe group consisting of alkali metal hydroxides and alkali metalcarbonates in an amount corresponding to 5 to 35 percent of the totalweight of said ether, water and material present in the mixture,maintaining said mixture at a temperature of about 25 C. to 60 C.whereby to effect the formation of an aqueous layer having a smallcontent of said ether and of an ether layer having a small content ofwater, and separating the said layers.

References Cited in the file of this patent Kobe et al.: Jour. PhysicalChemistry, vol. 44 (1940), pgs. 629-633.

1. IN THE SEPARATION OF A DIALKYL ETHER OF DIETHYLENE GLYCOL, WHEREINTHE ALKYL GROUPS CONTAIN ONE TO THREE CARBON ATOMS EACH, FROM AN AQUEOUSSOULATION THEREOF, THE PROCESS COMPRISING SUBSTANTIALLY SATURATING SAIDSOLUTION WITH AN ALKALI METAL CHLORIDE, ADMIXING A MATERIAL CHOSEN FROMTHE GROUP CONSISTING OF ALKALI METAL HYDROXIDES AND ALKALI METALCARBONATES IN AN AMOUNT CORRESPONDING TO 5 TO 35 PERCENT OF THE TOTALWEIGHT OF SAID ETHER, WATER AND MATERIAL PRESENT IN THE MIXTUREMAINTAINING SAID MIXTURE AT A TEMPERATURE OF ABOUT 25* C. TO 60* C.WHEREBY TO EFFECT THE FORMATION OF AN AQUEOUS LAYER HAVING A SMALLCONTENT OF SAID ETHER AND OF AN ETHER LAYER HAVING A SMALL CONTENT OFWATER, AND SEPARATING THE SAID LAYERS.